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Subject[PATCH 7/7] mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case
Date
In section_deactivate(), pfn_to_page() doesn't work any more after
ms->section_mem_map is resetting to NULL in SPARSEMEM|!VMEMMAP case.
It caused hot remove failure, the trace is:

kernel BUG at mm/page_alloc.c:4806!
invalid opcode: 0000 [#1] SMP PTI
CPU: 3 PID: 8 Comm: kworker/u16:0 Tainted: G W 5.5.0-next-20200205+ #340
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015
Workqueue: kacpi_hotplug acpi_hotplug_work_fn
RIP: 0010:free_pages+0x85/0xa0
Call Trace:
__remove_pages+0x99/0xc0
arch_remove_memory+0x23/0x4d
try_remove_memory+0xc8/0x130
? walk_memory_blocks+0x72/0xa0
__remove_memory+0xa/0x11
acpi_memory_device_remove+0x72/0x100
acpi_bus_trim+0x55/0x90
acpi_device_hotplug+0x2eb/0x3d0
acpi_hotplug_work_fn+0x1a/0x30
process_one_work+0x1a7/0x370
worker_thread+0x30/0x380
? flush_rcu_work+0x30/0x30
kthread+0x112/0x130
? kthread_create_on_node+0x60/0x60
ret_from_fork+0x35/0x40

Let's defer the ->section_mem_map resetting after depopulate_section_memmap()
to fix it.

Signed-off-by: Baoquan He <bhe@redhat.com>
---
mm/sparse.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/sparse.c b/mm/sparse.c
index 623755e88255..345d065ef6ce 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -854,13 +854,15 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
ms->usage = NULL;
}
memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr);
- ms->section_mem_map = (unsigned long)NULL;
}

if (section_is_early && memmap)
free_map_bootmem(memmap);
else
depopulate_section_memmap(pfn, nr_pages, altmap);
+
+ if(!rc)
+ ms->section_mem_map = (unsigned long)NULL;
}

static struct page * __meminit section_activate(int nid, unsigned long pfn,
--
2.17.2
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